Coating metals



Patented Sept. 8, 1936 UNITED. STATES PATENT, OFFICE No Drawing. Application December 22,1934, Serial No. 758,827

7 Claims. (Cl. 91-402) This invention relates to a method of coating metals, and more particularly to the hot-coating of one metal by'aiiother.

In the coating of a surface with molten metal it frequently becomes necessary to apply a protective coating upon the surface to protect it, for example from oxidation. For example, in the manufacture of bearings in which a steel or ferrous metal surface is coated with a molten layer of 10 some other metal, such as copper, it is essential that the steel be protected by a flux, particularly while it is being heated just before the coating op-- eration. The use of such a flux is attended by considerable difliculty in that it either tends to break off, or fails to wash ofi in advance of the metal coating.

It has now been discovered that these difficulties may be overcome if the surface to be coated is protected with a primary, high melt point flux which is still non-fluid, or at least viscous near the melting point of the coating metal, and the surface is then progressively coated with molten metal upon which is floated a second flux which will greatly lower the surface tension of the viscous flux so that it is completely and readily removed.

For example, in the manufacture of a bearing from a steel cylinder which is to be coated on the inside with a copper alloy, the interior of the cylinder is uniformly coated with a flux which will remain viscous at about the melting point of the copper alloy. This coating is preferably accomplished by suspending the flux in a volatile liquid,

rapidly revolving the cylinder, and applying the suspended flux therein so that it is uniformly coated by centrifugal force upon the inside of the cylinder and then drying the volatile liquid while so revolving the cylinder. Sometimes it is advisableto admit a current of hot air inside the ro- 40 tating cylinder during this process.

One end of the cylinder may then be closed, a core, such as a carbon core, inserted within it to leave the proper space for the copper coating,

and molten copper alloy admitted from the bottom, the cylinder being maintained in a vertical position.

Before the metal is admitted, however, the cylinder and core are heated approximately to the melting point of the alloy, and a fluxing material capable of markedly lowering the surface tension of the viscous flux is placed in the bottom of the cylinder in such manner that it floats upon the surface of the molten metal. The molten metal is then added, for example, through an opening in the core leading to the bottom of the cylinder calcium fluoride (CaFz).

or through other opening in the bottom, and thus progressively contacts the surface of the cylinder. As'the molten metal rises, it carries on its surface the secondary flux, which completely removes the primary flux as it touches it. In this manner it 5 is possible to obtain an adherent coating even in the case of ordinarily very difiicultly wet metal, such as steel and copper-lead alloys.

A preferred primary or viscous flux may be prepared by the use of sodium borate (NaZBAO'I) and 10 These materials should be extremely dry and anhydrous. In preparing the flux from them it is preferred to grind the ingredients, for example, in a porcelain ball mill while wet with anhydrous methanol, for a long 15 period, for example, about 48 hours. It is preferred that the grinding be continued until the materials are almost colloidal, and will remain in suspension for say one or two hours. After the creamy suspension is formed, it is preferred to 20 keep it in tightly corked bottles if it is not to be used within a short time.

The flux may then be applied either by dipping or as previously described by centrifugal action, and is dried in place.

A mixture of 25 parts of calcium fluoride and '75 parts of the borax glass is preferred, although a mixture of 20 parts of the fluoride and parts of the borax is substantially as good and a range of 15 to 30 parts of the fluoride and '70 to 30 parts of the borax glass is suitable for normaloperations.

The percentages of course depend to a considerable extent upon the melting point of the metal which is to be coated. 35

In case of the foregoing primary flux, a satisfactory secondary flux is anhydrous calcium fluoride in powdered form. It is not necessary to use an extremely fine powder for the secondary flux. 40

The primary flux is ordinarily applied to a depth of about 5th inch, and the ratio of primary to secondary flux is, ordinarily about 10 grams of primary flux to 8 to 10 grams of secondary. The ratio will depend to a great extent 45 upon the temperature of the molten metal.

The foregoing detailed description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as 50 broadly as permissible in view of the prior art.

What I regard as new, and desire to secure by Letters Patent, is:

1. The method as set forth in claim 4, in which the primary flux comprises a major portion of 56 proportion of flncly divided anhydrous calcium fluoride, and the secondary flux is. anhydrous calcium-fluoride. p

2. Afluxoomprising'IO-GB-partaofanhydrous flnely dividedsodium borate and 30-15 of anhydrous finely divided calcium fluoride.

'tAfluxassetforthin claim2 inwhichthe sodium borate is '15 partsand the calcium fluoride 4. In a process of hot-coating molten metal uponapreheatedmetallicmrfaoe,inwhichthe metallicsurfaceiscoatedwithaprimaryflux which, at the preheating is plastic enough to protect the surface and is viscous enough to maintain a protecting layer on a ver--.

tlcal wall of the surface, in which the flux-coated surface is preheated to about the melting point of the coating metal, and the flux coated surface is progressively immersed in the coating metal; the steps of floating upon the surface of the coating metal asecond flux having the property .6 am e of forming a free 'flowing flux with the primary flux, and pr l csaively immersing the flux-coated surface therein, whereby prior to or immediately upon'xentr'a-nce of the surface into the coating metal it is entirely free of fl 5. The method as set forth in claim 4 iii which the-surface is immersed in arising, continuously augmented body of molten coating metal having a molten secondary flux on. its upper surface,

wherein flux removed from the'flux-coated metallic'surface is floated upwardly.

, 6. The method as set forth in claim 4m which the primary flux comprisesa major portion of anhydrous flnely divided borax glass and a minor proportion of flnely divided anhydrous calcium fluoride, and the secondary flux is anhydrous calcium fluoride;

7. 'riiemetncd as set forth in claim 4- in which,

the coated surface is a ferrous metal surface, and

the molten metal hm melting point of the order of that of copper. V

CARL PFANSTIEHL. 

